1. Field of the Invention
The present invention concerns a method for manufacturing a cooling device for a gradient coil, the cooling device being of the type having at least one flexible cooling tube arranged on a carrier plate so as to be configured in a predetermined pattern.
2. Description of the Prior Art
A cooling device of the above type is known, for example, from DE 197 21 985 A1. It has a flexible cooling tube which can be made of metal or plastic, and which is laid out in a predetermined pattern on the course of the coil windings of the adjacent gradient coil group with which the cooling device is to be connected. The cooling tube—usually a number of plastic tubes which are connected to form separate cooling circuits—is attached to a suitable carrier plate that is designed to pro-vide electrical isolation, but is sufficiently flexible for the entire cooling device to be able to be bent if necessary if the gradient coil is a cylindrical coil. For fixing the cooling tube to the carrier plate, for example a glass rein-forced plastic plate, one method is to use elastic threads, meaning the tube or tubes are sewn onto the plate. However it is also conceivable for the cooling tube to be fixed to the carrier at a number of points using an adhesive.
Such a cooling device makes it possible to remove the heat arising during operation of the gradient coil. A gradient coil usually features a number of coils in order to create three magnetic field gradients standing at right angles to each other. With today's frequently used actively shielded gradient coils, in addition to the primary coil creating the useful field, secondary coils are present that prevent eddy currents that arise in metallic parts of a basic field magnet surrounding the gradient coil. These secondary coils are arranged concentrically around the primary coil and at a distance from this coil. Typically pulsed current on the order of magnitude of several hundred A, usually approx. 300 A, flows through each gradient coil. The ohmic resistance of the coil causes a considerable amount of energy to be converted into heat. To avoid excessive heating of the gradient coil and of the interior of the magnetic resonance de-vice in which the patient lies, this heat must be removed. This is done to great effect by a cooling device, as described in DE 197 21 985 A1.
Plastic tubes with a circular cross section, usually a PA tube, are used as cooling tubes for manufacturing such a cooling device, which are arranged on a carrier plate which is usually around 1 mm thick. Such a cooling device is fitted as described between the individual coil layers and molded together with the coil layers into a carrier matrix, for example made from epoxy resin. Typically a number of cooling tubes, each of approximately 100 m in length, are inserted for each coil in a number of parallel cooling circuits using a number of such cooling devices. As a result of the mandatory requirement for integration of the cooling device in the gradient coil, this arrangement has a considerable radial extent, which, due to the limited installation volume available for a gradient coil and the desire to make the patient chamber as large as possible, is not desirable. In addition there is always the desire to further improve the cooling performance.